Innovative method for removing bromine in waste printed circuit boards: Ultrafine milling and porous media loaded debromination agent

Resin is the main harmful substance in waste printed circuit boards (WPCBs) due to the presence of harmful bromine. In this study, the methods of ultrafine milling of resin and loading debromination agent on porous gasification slag were proposed to improve the debromination effect. The morphology, composition and phase of the gasification slag and resin were analyzed by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The results show that the residual carbon in the gasification slag has porous structure, which contributes to the loading of debromination agent. The specific surface area and porosity of gasification slag before and after acid treatment were analyzed by BET. Using the porous properties of gasification slag, different debromination agents were attached to prepare efficient debromination agents, which were adopted for thermal debromination of resin in WPCBs. Subsequently, ICP-MS was used to determine the content of bromine in pyrolysis residue. The results show that when FeCl₂/FeCl₃ was used as the debromination agent, the debromination efficiency was only 67.19% and 58.29%, while using gasification slag-FeCl₂/FeCl₃ composite, the debromination efficiency can be increased to 81.63% and 76.25%. Therefore, the cooperative treatment can realize the resource utilization of the two wastes.     

High strength and high porosity YB_2C_2 ceramics prepared by a new high temperature reaction/partial sintering process

Porous ultrahigh temperature ceramics(UHTCs) are potential candidates as reusable thermal protection materials of transpiration cooling system in scramjet engine. However, low strength and low porosity are the main limitations of porous UHTCs. To overcome these problems, herein, a new and simple in-situ reaction/partial sintering process has been developed for preparing high strength and high porosity porous YB_2C_2. In this process, a simple gas-releasing in-situ reaction has been designed, and the formation and escape of gases can block the shrinkage during sintering process, which is favorable to increase the porosity of porous YB_2C_2. In order to demonstrate the advantages of the new method, porous YB_2C_2 ceramics have been fabricated from Y_2O_3, BN and graphite powders for the first time. The as-prepared porous YB_2C_2 ceramics possess high porosity of 57.17%–75.26% and high compressive strength of 9.32–34.78 MPa.The porosity, sintered density, radical shrinkage and compressive strength of porous YB_2C_2 ceramics can be controlled simply by changing the green density. Due to utilization of graphite as the carbon source, the porous YB_2C_2 ceramics show anisotropy in microstructure and mechanical behavior. These features render the porous YB_2C_2 ceramics promising as a thermal-insulating light-weight component for transpiration cooling system.     

Preparation of porous Fe2O3/SiO2 nanocomposite abrasives and their chemical mechanical polishing behaviors on hard disk substrates

Abrasives play an important role in chemical mechanical polishing (CMP) processes. Compact solid silica particles, which have been widely used as abrasive in CMP slurries, may cause surface defects because of their high hardness. Porous silica abrasive exhibits better surface planarization and fewer scratches than traditional solid silica abrasive during the polishing of hard disk substrates. However, the improvement in material removal rate (MRR) was not significant. Therefore, porous Fe₂O₃/SiO₂ nanocomposite abrasives were prepared and their CMP performances on hard disk substrates were investigated. Experiment results indicate that the MRR of slurry containing porous Fe₂O₃/SiO₂ nanocomposite abrasives is obviously higher than that of slurry containing pure porous silica abrasive under the same testing conditions. MRR increases with the increase of the molar content of iron in porous Fe₂O₃/SiO₂ nanocomposite abrasives. Moreover, surfaces polished by slurries containing the porous Fe₂O₃/SiO₂ nanocomposite abrasives exhibit lower surface roughness, fewer scratches as well as lower topographical variations than that by pure porous silica abrasive.     

Novel alkali-resistant porous glass prepared from a mother glass based on the SiO2-B2O3-RO-ZrO2 (R = Mg,Ca, Sr,Ba and Zn) system

The alkali-resistant porous glass was prepared from the Si0₂-B₂0₃-RO (R=Mg, Ca, Sr, Ba and Zn) system containing Zr0₂. The porous glass skeleton contained 2–3 mass% Zr0₂ and the alkali resistance was greatly improved over that of ordinary Vycor-type porous glass. Because of the high alkali resistance, the elimination of the colloidal Si0₂ and Zr0₂ gelated during the acid leaching of the phase-separated glass, was promoted and as a result, a very sharp pore-size distribution of porous glass was attained. In addition, the limit of the available pore size of porous glass was widely expanded.     

Novel optical and structural properties of porous GaAs formed by anodic etching of n+-GaAs in a HF:C2H5OH:HCl:H2O2:H2O electrolyte: effect of etching time

Porous GaAs layers have been formed by anodic etching of n ⁺-type GaAs (10.0) substrates in a HF:C₂H₅OH:HCl:H₂O₂:H₂O electrolyte. A dramatic impact of etching time on the optical and structural properties of porous GaAs layer is demonstrated. The nano/micro-features of porous GaAs layers are revealed by scanning electron microscopy (SEM) imaging. Two-peak room temperature photoluminescence (PL), “blue-green” and “green-yellow”, is obtained in all prepared porous GaAs samples. Proper adjustment of etching time is found to produce a white color layer, instead of the usual dark gray color of porous GaAs. This is found to cause vast enhancement in the intensity of the visible PL in porous GaAs layer. Chemical composition and structural characterization by means of X-ray photoelectron spectroscopic (XPS), X-ray diffraction (XRD), and micro-Raman spectroscopy, confirm that this layer is characterized with monoclinic β-Ga₂O₃ rich surface. Etching time induced—modification of structural and chemical properties of porous GaAs layer is discussed and correlated to its PL behavior. It is inferred that the “blue-green” PL in porous GaAs can be ascribed to different degrees of quantum confinement in GaAs nanocrystallites, whereas, the “green-yellow” PL is highly influenced by the As₂O₃ and Ga₂O₃, content in the porous GaAs layer. In addition, the reflectance measurements reveal an anti-refection trend of behavior of porous GaAs layers in the spectral range (500–1,100 nm).     

Preparation and characterization of ZrO2 porous nanosolid and its composite fluorescent materials

ZrO₂ porous nanosolid has been successfully prepared by a novel hydrothermal hot-press (HHP) method, using ZrO₂ nanoparticles as the starting material. Furthermore, a kind of O, O-donating chelating regent, morin was assembled into the pores of ZrO₂ porous nanosolids, and a morin/ZrO₂ porous nanocomposite was obtained. Because of the interaction between morin molecules and the surface of ZrO₂ porous nanosolid, a blue-shift of the photoluminescence (PL) peak was observed in ZrO₂/morin nanocomposite by comparing with that of morin.     

Templated synthesis of ordered porous TiO2 films and their application in dye-sensitized solar cell

Ordered porous TiO₂ thin films were fabricated on conductive glass by using colloid crystal template of polystyrene (PS) spheres. Microstructural characterization by scanning electron microscopy techniques was carried out to explore the porous structural changes due to the PS templates which could be controlled by adjusting the drawing rate. Photovoltaic performance was measured and this revealed the effect of microstructural changes. The results showed that monolayer porous TiO₂ films and multilayer porous TiO₂ films could be successfully prepared. And multilayer porous TiO₂ films provided large surface area for dye absorption to increase the efficiency of dye-sensitized solar cells (DSSCs) which were assembled by porous TiO₂ films.     

Incorporation of transition metal in porous glass-ceramics of TiO2-SiO2 system

Incorporation of transition metals in porous glass-ceramics of TiO₂-SiO₂ system was made by the phase separation and crystallization of the glasses of TiO₂-SiO₂-Al₂O₃-P₂O₅-CaO-MgO system containing various kinds of transition metals. The amount of transition metals incorporated in the skeleton of the porous glass-ceramics was dependent on both chemical composition of mother glass and conditions of heat treatment. In general the amount decreased with the increasing amount of rutile in the skeleton. In the glass of high TiO₂/SiO₂ ratio, the incorporation of relatively large amounts of transition metals was possible even if the precipitation of a fairly large amount of rutile occurred. The crystallization of rutile and in porous glass-ceramics was essential to fabricate rigid platelet porous glass-ceramics.     

Comparison of gas sensing properties based on hollow and porous α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanotubes

Hollow and porous α-Fe₂O₃ nanotubes were successfully synthesized by single nozzle electrospinning method followed by annealing treatment. The crystal structures and morphologies of the as-prepared materials were characterized by X-ray diffraction and scanning electron microscopy, respectively. The as-prepared materials were applied to construct gas sensor devices which gas sensing properties were further investigated. The obtained results revealed that porous α-Fe₂O₃ nanotube gas sensors exhibit a markedly enhanced gas sensing performance compared with hollow α-Fe₂O₃ nanotube gas sensors, which was about three times higher to 100 ppm acetone at 240 °C. Interestingly, hollow and porous α-Fe₂O₃ nanotube gas sensors both showed fast response–recovery time and good selectivity, but the porous ones possessed the shorter recovery time. The improved properties could be attributed to the unique morphology of porous nanotubes. Thus, further improvement of performance in metal-oxide-semiconductors materials could be realized by preparation the unique porous structures of nanotubes. Moreover, it is expected that porous metal-oxide-semiconductors nanotubes could be further design as promising candidates for gas sensing materials.     

Synthesis and characterization of TiO<Subscript>2</Subscript>-incorporated silica foams

Titania-incorporated silica (TiO₂–SiO₂) porous materials have great applications in diverse areas. In this work, TiO₂–SiO₂ porous materials with tunable Si/Ti molar ratio (R) have been successfully prepared through a one-pot method under a near-neutral condition. With decreasing Si/Ti R, a phase transition from a macroporous foam-like structure to mesostructure is observed. The resultant TiO₂–SiO₂ porous materials possess large surface areas and high pore volumes. In addition, the titania species are homogenously dispersed in silica matrix when Si/Ti R ≥ 10. Our contribution provides a convenient method to synthesize TiO₂/SiO₂ porous materials with very large pore size, high pore volume, and relatively high titania content well dispersed in the silica wall framework.     

Porous Gold Nanoshells on Functional NH2‐MOFs: Facile Synthesis and Designable Platforms for Cancer Multiple Therapy

AuroShell nanoparticles (sealed gold nanoshell on silica) are the only inorganic materials that are approved for clinical trial for photothermal ablation of solid tumors. Based on that, porous gold nanoshell structures are thus critical for cancer multiple theranostics in the future owing to their inherent cargo‐loading ability. Nevertheless, adjusting the diverse experimental parameters of the reported procedures to obtain porous gold nanoshell structures is challenging. Herein, a series of amino‐functionalized porous metal–organic frameworks (NH₂‐MOFs) nanoparticles are uncovered as superior templates for porous gold nanoshell deposition (NH₂‐MOFs@Au_shell) by means of a more facile and general one‐step method, which combines the enriched functionalities of NH₂‐MOFs with those of porous gold nanoshells. Moreover, in order to illustrate the promising applications of this method in biomedicine, platinum nanozymes‐encapsulated NH₂‐MOFs are further designed with porous gold nanoshell coating and photosensitizer chlorin e6 (Ce6)‐loaded nanoparticles with continuous O₂‐evolving ability (Pt@UiO‐66‐NH₂@Au_shell‐Ce6). The combination of photodynamic and photothermal therapy is then carried out both in vitro and in vivo, achieving excellent synergistic therapeutic outcomes. Therefore, this work not only presents a facile strategy to fabricate functionalized porous gold nanoshell structures, but also illustrates an excellent synergistic tumor therapy strategy.     

Properties of porous Si3N4 ceramic electromagnetic wave transparent materials prepared by technique combining freeze drying and oxidation sintering

A simple and low-cost technique combining freeze drying and oxidation sintering is explored to prepare Si₃N₄ ceramics with high porosity and complex shape. The effects of sintering temperature and time on the phase composition, microstructure, porosity, pore size and dielectric constant of the porous Si₃N₄ ceramics are studied. Due to the variations of phase composition and microstructure, the porous Si₃N₄ ceramics sintered at different temperature possess characteristic in flexural strength. The porous Si₃N₄ ceramics sintered at 1,300 °C for 2–3 h have the highest flexural strength of 71–74 MPa. The changes of porosity and composition have much effect on the dielectric constant of porous Si₃N₄ ceramics. Because of the high porosity and SiO₂ volume fraction, the porous Si₃N₄ ceramics sintered at 1,300 °C for 2–3 h possess low dielectric constant of 3.4–3.6 and small pore size of 0.9 μm. The porous Si₃N₄ ceramics are good structural/functional and promising electromagnetic wave transparent material.     

Fabrication of porous TiO2 nanofiber and its photocatalytic activity

Porous TiO₂-based nanofiber was fabricated via a combined electrospinning and alkali-dissolution method. TiO₂/SiO₂ composite nanofiber was firstly prepared by electrospinning and sintering, and then silica was leached out with alkaline solution from the bulk of TiO₂/SiO₂ composite nanofiber to produce porous microstructure. The thermal decomposition and phase structure of the composite nanofiber precursor was investigated with TG/DSC and XRD, and optimal sintering temperature was obtained. SEM-EDX and FT-IR characterization show that most silica can be dissolved out from the composite nanofiber and thus porous nanofiber with excellent microstructure can be spontaneously formed. The effect of composite nanofiber composition on porous microstructure was studied, and it is found that the composite nanofiber with 20wt% silica can produce better porous microstructure compared to those with 10wt% and 30wt% silica. Meanwhile, porous TiO₂ nanofiber with 20wt% silica shows higher degradation efficiency to Congo Red.     

Preparation and properties of mullite-bonded porous SiC ceramics using porous alumina as oxide

Mullite-bonded porous silicon carbide ceramics were prepared by an in situ reaction bonding technique and sintering in air with SiC, porous Al₂O₃, and graphite as starting materials. The pores in the ceramics were formed by burning graphite and by stacking particles of SiC and Al₂O₃. The surface of SiC was oxidized to SiO₂ at high temperature. With a further increase in temperature, SiO₂ reacted with Al₂O₃ to form mullite. The reaction-bonding characteristics, phase composition, open porosity, mechanical strength as well as the microstructure of porous SiC ceramics were investigated.     

Synthesis of micron-sized porous CeO2SiO2 composite particles for ultraviolet absorption

Micron-sized porous composite particles composed of CeO₂ and SiO₂ nanoparticles were prepared for a UV absorption application by an aerosol spray-drying process from as-prepared CeO₂ nanoparticles, commercial SiO₂, and a polystyrene latex template. The morphology, structure crystallinity and pore size distribution of the as-prepared porous CeO₂SiO₂ composite particles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Barrett-Joyner-Halenda (BJH) method, respectively. The porous CeO₂SiO₂ composite particles, with diameters of approximately 10 μm, showed a spherical morphology. As the contents of CeO₂ in the precursor was increased from 0.25 wt% to 1.5 wt%, we observed a change in the morphology of the composite particles from compactly packed porous particles to loosely packed porous particles. The as-prepared CeO₂SiO₂ composite particles were composed of meso- and macropores in the range of 3–200 nm. The effect of the CeO₂ content on the porous composite particles in terms of the UV absorption properties was also investigated by UV-visible spectroscopy. When the content of CeO₂ exceeded 0.75 wt% in the precursor, the particles showed higher UV absorption values compared to those of commercial TiO₂ nanoparticles. The as-prepared porous CeO₂SiO₂ composite particles can therefore be promising materials given their high UV absorption value.     

Synthesis and characterization of porous platelet-shaped α-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> with enhanced photocatalytic activity for 17α-ethynylestradiol

The porous platelet-shaped α-Bi₂O₃ photocatalyst was successfully synthesized by a novel hydrothermal–calcination method assisted with ethylenediamine and polyvinylpyrrolidone. The physical and chemical properties of α-Bi₂O₃ photocatalyst were characterized based on XRD, XPS, SEM, TEM, EDS, UV–Vis DRS, and PL techniques. The influence of preparation conditions on the formation of α-Bi₂O₃ photocatalyst was investigated, and the effect of catalyst dosage and pH value on the EE2 removal rate was also investigated. The synthesized porous platelet-shaped α-Bi₂O₃ photocatalyst exhibited excellent photocatalytic activity for 17α-ethynylestradiol (EE2), and 97.8% of EE2 was removed after 75 min of visible light irradiation using α-Bi₂O₃ as photocatalyst. The reaction rate constant over the porous platelet-shaped α-Bi₂O₃ photocatalyst was 11.6 and 11.4 times of that of traditional α-Bi₂O₃ and N-TiO₂, respectively. The possible photocatalytic mechanism has been discussed on the basis of the theoretical calculation and the experimental results. The porous platelet-shaped α-Bi₂O₃ was a stable and efficient photocatalyst, proving that it is a promising photocatalyst.     

Polyethyleneimine-loaded bimodal porous silica as low-cost and high-capacity sorbent for CO2 capture

In this work, bimodal (meso-macro) porous silicas with different mesopore diameters synthesized by using rice husk ash as a low-cost silica source and chitosan as a natural template were used as a polyethyleneimine (PEI) support for CO₂ capture. Unimodal porous silica supports with equivalent mesopore diameters to bimodal porous silica supports have been prepared for purpose of comparison. Effects of different PEI contents (10, 20, 30, 40 and 50 wt%) on CO₂ sorption capacity have been systematically investigated. The porous silica supports and the PEI-loaded porous silica supports were characterized by N₂-sorption analysis, scanning electron microscopy, Fourier transform infrared spectroscopy and thermal gravimetric analysis. CO₂ sorption measurements of all PEI-loaded porous silica supports were performed at different adsorption temperatures (60, 75, 85, 90, 95 and 105 °C). At low PEI contents (10–20 wt%), the CO₂ sorption of all adsorbents was found to decrease as a function of adsorption temperature, which was a characteristic of a thermodynamically-controlled regime. A transition from the thermodynamically-controlled regime to a kinetically-controlled regime was found when the PEI content was increased up to 30 wt% for PEI-loaded unimodal porous silicas and 40 wt% for PEI-loaded bimodal porous silicas. At high PEI contents (40–50 wt%), the CO₂ capturing efficiency of the PEI-loaded bimodal porous silicas was found to be considerably greater than that of the PEI-loaded unimodal porous silicas, indicating that most of the amine groups of PEI molecules loaded on the unimodal porous silica supports was useless, and thus the appeared macroporosity of the bimodal porous silica supports could provide a higher effective amine density to adsorb CO₂.     

Fabrication of porous TiO2 film via hydrothermal method and its photocatalytic performances

Porous anatase (TiO₂) films were fabricated onto stainless steel substrates with Ti(OC₄H₉)₄ as a precursor via hydrothermal process. The crystallization and porous structure of TiO₂ film were dependent on the time and temperature of the hydrothermal reaction. A TiO₂ film with orderly porous structure and high crystallization was obtained upon treatment at 150 °C for 2 h. The grain size of TiO₂ is ca. 6 nm, and pore diameter is ca. 10 nm. Diffusion of Fe into the porous TiO₂ film occurred; Fe also diffused onto the surface of the film with the extension of hydrothermal reaction time or increase of the reaction temperature. The diffusion reaction has a large effect on the formation of porous TiO₂ film as well as its interface texture. However, it does not change the crystal phase of the TiO₂. The resultant TiO₂ film showed high photocatalytic activity towards degradation of gaseous formaldehyde.     

Synthesis of porous titania thin films using carbonatation reaction and its hydrophilic property

Super-hydrophilic porous titania thin films containing mesoscale channels were successfully synthesized by the carbonatation reaction. An amorphous Li-Ti-O film with a smooth surface was prepared on a glass substrate by radio frequency magnetron sputtering using a Li₂TiO₃ target in an Ar atmosphere. The as-deposited films were carbonated at 400 °C for 10 h in CO₂, resulting in the formation of Li₂CO₃ and the development of characteristic through-channels. After dissolution of the Li₂CO₃ in distilled water, porous TiO₂ thin films with mesoscale through-channels were fabricated. The obtained porous films had a large surface area and show a rapid decrease in the water contact angle or excellent super-hydrophilicity.